Quantitative analysis of abnormal spontaneous behavior and clinical assessment of the stargazer rat

A new mutant derived from the Zucker rat strain called stargazer (homozygous stg/stg) displays abnormal behavior that is characterized by pronounced arching of the neck ("stargazing"), rapid circling, and conspicuous hyperactivity. Results of serologic assays performed by two independent diagnostic laboratories have indicated that the abnormal behavior in the stargazer is not the result of a viral or bacterial infection. In this report, different groups of stargazer rats and their normal-behaving littermates (heterozygous stg/+) were assessed with regard to spontaneous behaviors, heart rate, blood pressure, and plasma biochemical profiles. Besides frequent stargazing, the predominant behavioral feature of the stargazers was extreme hyperactivity; they had sevenfold greater activity than the normal littermates (P < 0.05), expressed in the form of rapid ambulation and tail-chasing. The stargazers had significantly greater daily calorie and water consumption, despite being significantly smaller in body weight than the littermates (P < 0.05 for all). However, urine output was not different between the two groups. Heart rate and blood pressure also were not different. Stargazers had significantly lower total triglycerides concentration and lower aminotransferase activity than littermates (P < 0.05 for both), a finding probably related to their smaller body size. It is concluded that stargazer rats are extremely hyperactive but normotensive; heterozygous littermates are behaviorally normal, despite being carriers of the stg gene; and routine diagnostic blood testing revealed no important differences between the stargazers and their unaffected littermates.